esp8266/esp_mphal: Add support for debug UART-only output.

Helpful when debugging dupterm support (because otherwise all output is
spooled to dupterm too).

To use:

mp_printf(&mp_debug_print, "...");

esp8266/esp_mphal.c

@@ -39,6 +39,9 @@ extern void ets_wdt_disable(void);
 extern void wdt_feed(void);
 extern void ets_delay_us();
 
+void mp_hal_debug_tx_strn_cooked(void *env, const char *str, uint32_t len);
+const mp_print_t mp_debug_print = {NULL, mp_hal_debug_tx_strn_cooked};
+
 void mp_hal_init(void) {
     ets_wdt_disable(); // it's a pain while developing
     mp_hal_rtc_init();
@@ -74,6 +77,15 @@ void mp_hal_stdout_tx_char(char c) {
     mp_uos_dupterm_tx_strn(&c, 1);
 }
 
+#if 0
+void mp_hal_debug_str(const char *str) {
+    while (*str) {
+        uart_tx_one_char(UART0, *str++);
+    }
+    uart_flush(UART0);
+}
+#endif
+
 void mp_hal_stdout_tx_str(const char *str) {
     while (*str) {
         mp_hal_stdout_tx_char(*str++);
@@ -95,6 +107,16 @@ void mp_hal_stdout_tx_strn_cooked(const char *str, uint32_t len) {
     }
 }
 
+void mp_hal_debug_tx_strn_cooked(void *env, const char *str, uint32_t len) {
+    (void)env;
+    while (len--) {
+        if (*str == '\n') {
+            uart_tx_one_char(UART0, '\r');
+        }
+        uart_tx_one_char(UART0, *str++);
+    }
+}
+
 uint32_t mp_hal_ticks_ms(void) {
     return system_get_time() / 1000;
 }

esp8266/esp_mphal.h

@@ -27,6 +27,10 @@
 #ifndef _INCLUDED_MPHAL_H_
 #define _INCLUDED_MPHAL_H_
 
+struct _mp_print_t;
+// Structure for UART-only output via mp_printf()
+extern const struct _mp_print_t mp_debug_print;
+
 void mp_hal_init(void);
 void mp_hal_rtc_init(void);
 void mp_hal_feed_watchdog(void);